That Kant suffered from depression may come as a surprise, especially given the ambition of his philosophical books and the enthusiasm of his wide-ranging intellectual interests (his lecture courses cover everything from philosophical logic to anthro- pology to chemistry to predictions about the end of the world). But in 1798, in a letter to a colleague on the topic of “the art of prolonging human life,” Kant commented on his own struggle with depression. The comments are rare for Kant, both in the sense of being personal and in the way they serve as a confession of weakness. In typical fashion, Kant first defines depression as “the weakness of abandoning oneself despondently to general morbid feelings that have no definite object (and so making no attempt to master them by reason).” A thought without an object is a troubling thing in Kant’s philosophy; it can lead to endless train of fickle thoughts without any ground, similar to the speculative debates in Kant’s time over the existence of God, the origin of the universe, or the existence of a soul. Reason becomes employed for no reason – or at least, for no good reason. At issue for Kant is not just the employment of reason over faith or imagination, but the instrumental use of reason – reason mastering itself, including its own limitations. This was as much the case for everyday thought as it was for philosophical thinking: “The opposite of the mind’s self-mastery… is faint- hearted brooding about the ills that could befall one, and that one would not be able to withstand if they should come.”

And when the coherence of reason is threatened, so is philosophy. Or rather, so is the philosopher. A little later on, Kant offers this strange confession: “I myself have a natural disposition to hypochrondria because of my flat and narrow chest, which leaves little room for the movement of the heart and lungs; and in my earlier years this disposition made me almost weary of life.”

Elsewhere Kant drops hints of this depression. In the Critique of Judgement, for instance, he allows that “misanthropy” is preferable, and even has the character of the sublime: “Falsehood, ingratitude, injustice, the puerility of the ends which we ourselves look upon as great and momentous… these all so contradict the idea of what men might be if they only would, and are so at variance with our active wish to see them better, that, to avoid hating where one cannot love, it seems but a slight sacrifice to forego all the joys of fellowship with our kind.”

But Kant does not give in so easily to this “pathology” of thought. Philosophy is the panacea. Kant distinguishes “philosophizing” from “philosophy,” though both play a therapeutic role in reason’s self-mastery. Philosophizing, for Kant, “does not involve being a philosopher,” but instead “is a means of warding off many disagreeable feelings and, besides, a stimulant to the mind that introduces an interest into its occupations.” At another level, there is “philosophy” proper, “whose interest is the entire final end of reason (an absolute unity),” and which “brings with it a feeling of power which can well compensate to some degree for the physical weaknesses of old age by a rational estimation of life’s value.”